The present invention relates to the art of electrical cables and, in particular, to an electrical cable having a flat configuration particularly suitable for use in smaller diameter oil wells where the atmosphere is at elevated temperatures and pressures, and is corrosive. It will be appreciated, however, that the invention has broader applications and may be adapted to other cable applications and uses.
Prior art oil well cables have been designed for use in corrosive, high temperature, and high pressure conditions. Such cables are typically formed with a plurality of conductors, each of which is surrounded by a polymeric insulating material, such as an ethylene-propylene-diene monomer terpolyer (EPDM), with an optional layer of a polyimide plastic often disposed between the conductor and the EPDM. EPDM comprises an elastomer rubber which is permeable by gases in the well. Pressure changes experienced by the cable, as it is thereafter removed from a well, can cause the EPDM material to enlarge or swell. Thus, a braid overwrap has also been provided in some prior art teachings to prevent rupture of the EPDM as a result of swelling. An alternative to wrapping a braid around EPDM insulation to restrain swelling is to encase the insulated conductor in lead. This prevents well gases from reaching the EPDM. Either the lead encased or braid-wrapped conductors may also include an outer wrap of metal or plastic armor. Examples of cables embodying these concepts are shown in U.S. Pat. Nos. 3,809,802; 4,088,830; 4,096,351; and 4,284,841.
Cables used in an oil well type environment are subject not only to chemical attack, but also to mechanical abuse from being installed into and removed from the well itself. Although the lead sheathed cables are not as vulnerable to chemical attack as braid-wrapped cables, the weight of the lead renders mechanical failure far more likely. Moreover, handling of lead sheathed cables is difficult.
While cables having EPDM with a braid overwrap are generally lighter in weight than the lead sheathed cables, they also are subject to mechanical damage, and particularly to so-called embolisms caused by the expansion of entrapped gases on depressurization. One proposed solution was the use of a restraining braid to prevent failure in conjunction with the elimination of any jacket that would add an interface to entrap gases. The problem with this solution is that the insulating material has little or no protection from well fluids and the restraining braid has no protection from abrasion or other mechanical or chemical damage prior to or during the armoring process or while in an oil well.
It has, therefore, been considered desirable to develop a new submersible electrical cable construction. The subject invention is directed to such development which overcomes the foregoing problems and others, and which is deemed to better meet the needs of the industry.